Gerald Holmes, California Polytechnic State University at San Luis Obispo, Bugwood.org

While some powdery mildews attack a very few specific plants, others have a broad host range and infect many different plants. It is important to recognize this because if a particular powdery mildew is infecting a plant in your nursery or greenhouse, you need to know what other plants might be at risk to the fungus as you decide what plants should be treated with a fungicide.